From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Guo Subject: Re: [PATCH 19/26] KVM: PPC: Book3S PR: always fail transaction in guest privilege state Date: Tue, 30 Jan 2018 11:11:23 +0800 Message-ID: <20180130031123.GG3261@simonLocalRHEL7.x64> References: <1515665499-31710-1-git-send-email-wei.guo.simon@gmail.com> <1515665499-31710-20-git-send-email-wei.guo.simon@gmail.com> <20180123083033.GK3924@fergus.ozlabs.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org To: Paul Mackerras Return-path: Received: from mail-pf0-f194.google.com ([209.85.192.194]:45600 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752131AbeA3DL3 (ORCPT ); Mon, 29 Jan 2018 22:11:29 -0500 Content-Disposition: inline In-Reply-To: <20180123083033.GK3924@fergus.ozlabs.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Hi Paul, On Tue, Jan 23, 2018 at 07:30:33PM +1100, Paul Mackerras wrote: > On Thu, Jan 11, 2018 at 06:11:32PM +0800, wei.guo.simon@gmail.com wrote: > > From: Simon Guo > > > > Currently kernel doesn't use transaction memory. > > And there is an issue for privilege guest that: > > tbegin/tsuspend/tresume/tabort TM instructions can impact MSR TM bits > > without trap into PR host. So following code will lead to a false mfmsr > > result: > > tbegin <- MSR bits update to Transaction active. > > beq <- failover handler branch > > mfmsr <- still read MSR bits from magic page with > > transaction inactive. > > > > It is not an issue for non-privilege guest since its mfmsr is not patched > > with magic page and will always trap into PR host. > > > > This patch will always fail tbegin attempt for privilege guest, so that > > the above issue is prevented. It is benign since currently (guest) kernel > > doesn't initiate a transaction. > > > > Test case: > > https://github.com/justdoitqd/publicFiles/blob/master/test_tbegin_pr.c > > > > Signed-off-by: Simon Guo > > You need to handle the case where MSR_TM is not set in the guest MSR, > and give the guest a facility unavailable interrupt. Thanks for the catch. > > [snip] > > > --- a/arch/powerpc/kvm/book3s_pr.c > > +++ b/arch/powerpc/kvm/book3s_pr.c > > @@ -255,7 +255,7 @@ static inline void kvmppc_save_tm_sprs(struct kvm_vcpu *vcpu) > > tm_disable(); > > } > > > > -static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) > > +inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) > > You should probably remove the 'inline' here too. OK. BR, - Simon From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Guo Date: Tue, 30 Jan 2018 03:11:23 +0000 Subject: Re: [PATCH 19/26] KVM: PPC: Book3S PR: always fail transaction in guest privilege state Message-Id: <20180130031123.GG3261@simonLocalRHEL7.x64> List-Id: References: <1515665499-31710-1-git-send-email-wei.guo.simon@gmail.com> <1515665499-31710-20-git-send-email-wei.guo.simon@gmail.com> <20180123083033.GK3924@fergus.ozlabs.ibm.com> In-Reply-To: <20180123083033.GK3924@fergus.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Paul Mackerras Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org Hi Paul, On Tue, Jan 23, 2018 at 07:30:33PM +1100, Paul Mackerras wrote: > On Thu, Jan 11, 2018 at 06:11:32PM +0800, wei.guo.simon@gmail.com wrote: > > From: Simon Guo > > > > Currently kernel doesn't use transaction memory. > > And there is an issue for privilege guest that: > > tbegin/tsuspend/tresume/tabort TM instructions can impact MSR TM bits > > without trap into PR host. So following code will lead to a false mfmsr > > result: > > tbegin <- MSR bits update to Transaction active. > > beq <- failover handler branch > > mfmsr <- still read MSR bits from magic page with > > transaction inactive. > > > > It is not an issue for non-privilege guest since its mfmsr is not patched > > with magic page and will always trap into PR host. > > > > This patch will always fail tbegin attempt for privilege guest, so that > > the above issue is prevented. It is benign since currently (guest) kernel > > doesn't initiate a transaction. > > > > Test case: > > https://github.com/justdoitqd/publicFiles/blob/master/test_tbegin_pr.c > > > > Signed-off-by: Simon Guo > > You need to handle the case where MSR_TM is not set in the guest MSR, > and give the guest a facility unavailable interrupt. Thanks for the catch. > > [snip] > > > --- a/arch/powerpc/kvm/book3s_pr.c > > +++ b/arch/powerpc/kvm/book3s_pr.c > > @@ -255,7 +255,7 @@ static inline void kvmppc_save_tm_sprs(struct kvm_vcpu *vcpu) > > tm_disable(); > > } > > > > -static inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) > > +inline void kvmppc_restore_tm_sprs(struct kvm_vcpu *vcpu) > > You should probably remove the 'inline' here too. OK. BR, - Simon